For loom shed formation or shedding in weaving machines it is known in the prior art to provide a shedding device in which several shedding elements, which each respectively guide a warp thread sheet or group, are driven to move upwardly and downwardly via an intermediate transmission from the main drive motor of the weaving machine. In this manner a loom shed, which is formed by the warp thread sheets of different shedding elements, is alternately opened and closed. A weft thread is inserted into the opened loom shed. After the weft insertion, the loom shed is closed and then again opened with the aid of the shedding elements. Simultaneously the weft thread is beat-up against a fabric edge by a weaving reed and the process begins anew. A weave design or pattern is formed by the shed changes of the various different warp thread sheets and the insertion of different weft threads.
When closing and subsequently opening the loom shed it occurs that individual warp threads of neighboring warp thread sheets get caught or tangled or hung-up on one another. No loom shed is formed between these warp threads. In the subsequent weft insertion, these so called sticking or jammed or tangled warp threads cause interferences. In the weft insertion by means of mechanical elements, for example a gripper, the sticking warp threads are destroyed or broken by the weft insertion element, the weaving machine stops automatically due to warp break. In the weft insertion by means of a fluid jet, for example compressed air, the weft thread gets caught or hung up on the sticking warp threads. This leads to an automatic shut-down of the weaving machine due to weft break. Weft break and warp break lead to standstill times or down times of the weaving machine and make interventions by the personnel necessary. Therefore efforts are being made to prevent the sticking or tangling or jamming of warp threads. This is achieved, for example, in that the time points at which the loom shed is closed are prescribed differently for different neighboring warp thread sheets. Thereby it is achieved that all upwardly and downwardly moving warp threads do not encounter one another at the same time point in the closed loom shed, but rather that this encountering or meeting of warp thread sheets that are guided by different shedding elements takes place at different time points in the motion cycle of the weaving machine. However, in the prior art there are shedding devices for which this is not possible, because all shedding elements always simultaneously move through the shed closed position (loom shed closed) due to structural or constructive reasons.
The time point at which the shed closed position is run through can be changed in most shedding devices in that the connection between the main motor of the weaving machine and the shedding device driven from this main motor is released and then again connected after a turning or twisting of one of the two drive shafts. Thereby, the relative shed closure time point for all shedding elements and thus for all warp threads in the loom shed is changed within the motion cycle of the weaving machine. Such an adjustment of the relative shed closure time point for all shedding elements simultaneously can be carried out without mechanical intervention, that is to say also with a running weaving machine, in shedding devices that are driven by their own shedding motor. Such a change of the synchronicity between the main motor of the weaving machine and the shedding motor of the shedding device is carried out with the aid of electronic control signals of a control device of the weaving machine.
A weaving machine with the mentioned devices, which permit the changing of the synchronicity on a running weaving machine, is shown by the WO2003071017 A for example. In this document it is explained that with such a machine it is basically or fundamentally possible to flexibly arrange or establish the tuning or adaptation of the operating relationship of the weaving machine and the shedding device or shedding machine corresponding to the weaving requirements, that is to say to select within broad boundaries the synchronicity of both drive systems with respect to the basic or ground tuning or adaptation (e.g. shed closure at what weaving machine position angle) and with respect to the permissible tolerances. Furthermore, the WO2003071017 A discloses that the drive of the weaving and shedding machine is driven synchronously at a prescribed point, weaving cycle for weaving cycle. This point can be different weaving cycle for weaving cycle.
When working with such a weaving machine it has been determined in a surprising manner, that the problems described above in the introduction due to sticking or jamming warp threads can be reduced by certain or particular changes of the synchronicity on a running weaving machine.